I saw on television, say George Bush shoot by many photographer. Maybe 40 of them, all using camera with flash. We can see he is under flash rain. He may blind for a while .
In TTL mode (iTTL, eTTL or other method), we know that pre-flash will determine flash output. Even A or AA mode will determine if the flash illumination is enough for subject. Did flash illumination accuracy affected by other flash (rain flash)?